1. Field of the Invention
This invention pertains to methods and apparatus for applying elastic ribbons to webs of material, and more particularly to methods and apparatus for applying discrete lengths of stretched elastic ribbon to predetermined areas of a continuously moving web.
2. Description of the Prior Art.
The development of adult and infant disposable diapers is summarized in the article "New Trends in Adult Pads and Infant Diapers," by Francis J. Bouda, Non-Woven Industry, January 1983. Modern disposable diapers employ elastic ribbons, especially in the crotch area, to assist in preventing leakage of body discharges around the wearer's legs.
Various equipment has been developed to deal with the problems associated with handling the elastic ribbons applied to the sheets of diaper material. One problem is the holding of discrete lengths of elastic ribbons in the proper location during the manufacturing operation. The use of vacuum systems to hold the pieces to elastic ribbon is well known and is illustrated in U.S. Pat. Nos. 4,360,398; 4,379,016; and 4,397,704. However, vacuum systems are expensive to build and operate, and they do not provide positive retention of the ribbons.
An associated problem concerns the requirement that the elastic ribbon be applied to the moving web of diaper material such that when the ribbons are relaxed they bunch up the diaper to snug the wearer's legs. One solution to this problem is to corrugate the web material and to apply discrete pieces of elastic ribbon in a relaxed state to the peaks of the corrugations, as disclosed in U.S. Pat. Nos. 4,379,016 and 4,397,704. These designs have the advantage of utilizing only as much ribbon material as is necessary. However, the grooved drums required for corrugating the web are costly to manufacture, as is the vacuum system required to retain the web within the drum corrugations.
A second solution is to attach the elastic ribbons when in the stretched condition to the underlying webs. U.S. Pat. Nos. 4,081,301 and 4,360,398 exemplify this approach. The disadvantage is that a portion of elastic ribbon material is wasted because typically the elastic ribbons are applied only to the crotch regions of the diaper. It has been calculated that 50% of elastic material is wasted by this method. That represents a loss of $75,000.00 per year in some instances. The apparatus of U.S. Pat. No. 4,227,952 applies a stretched elastic ribbon to the web in a manner that does not waste ribbon material, but that apparatus is complicated to manufacture and maintain.
U.S. Pat. No. 3,694,815 utilizes a cryogenic bath in which a stretched elastic ribbon is immersed, thereby immobilizing the ribbon for attaching to the garment fabric; upon warming, elastic ribbon acquires its elastic properties.
U.S. Pat. No. 4,284,454 teaches methods and apparatus for mechanically gripping length of elastic ribbon for transverse placement on a continuous fabrication line. It is evident that the equipment of the U.S. Pat. No. 4,284,454 is complicated and costly.
Thus, a need exists for simple and economical apparatus which handles and attaches discrete pieces of elastic ribbon without waste to a continuously moving web.